I want to see what you think about this, Aldbigbang. I am going to change your 'OF'S' to "in" as in added into... I am also shortening the sentence a great deal, because repeating long phrases unnecessarily, can make people think there is more being said than there is (when you repeat long phrases unnecessarily.) :) The results indicated that ________ can be an effective active component IN whitening toothpaste and varying THE amount of _________ showed a significant difference on its effectiveness.

Much to the displeasure of the London Tube, I shall not mind the gaps. :) The results indicated that ________ can be an effective active component of whitening toothpaste and varying the amount of _________ showed a significant difference in its effectiveness as an active component of whitening toothpaste. The collocation is "a difference IN". You were probably thinking of "an effect ON". :)

.....varying amountS.... Otherwise OK.